1. Field of the Invention
This invention relates to a bipolar transistor and the method of producing the same. More particularly, it relates to a bipolar transistor and the method of producing the same, wherein a graft base region is formed in the semiconductor substrate by diffusion of impurities from a base contact electrode selectively formed on the semiconductor substrate.
2. Prior Art
For achieving a high speed and performance bipolar transistor, it is essential that the base width W.sub.B be narrow and that the base resistance Rbb' be small.
For realization of the high performance bipolar transistor, a technique of forming a link impurity diffusion region between an intrinsic base region which forms an active region and a graft base region formed by diffusing impurities from the base contact electrode has been proposed. This technique is disclosed for example in the Japanese Patent Application Nos. 184898/1987, 188025/1987 and 188026/1987.
However, in the technique of linking the intrinsic base region and the graft base region by the link impurity diffusion region, injuries to the structure may occur at the time of implanting ions so as to form the link impurity diffusion region. Such injuries caused by ion implantation promote accelerated diffusion in the active region or produce adverse effects by causing channeling tail. The result is that the base depth may be increased depending on the subsequent annealing.
The aforementioned Japanese Patent Application No. 184898/1987 discloses a method for producing a bipolar transistor wherein a sidewall is formed on the lateral side of the base contact electrode and a substrate portion is removed by taking advantage of this sidewall to form minute base and emitter regions. However, the adverse effect of side injection of the emitter and the base becomes predominant which interferes with the high speed operation of the transistor.